1. Technical Field
This invention pertains generally to signal acquisition, and more particularly to neural signal acquisition.
2. Background Discussion
Chronic brain-computer interfaces are an emerging technology that aim at restoring motor or communication function in individuals with spinal chord injuries and/or neurodegenerative diseases. Electrocorticography (ECoG) is a brain-recording modality that utilizes non-penetrating (e.g. sub-dural or epidural electrodes), and shows particular promise for future brain computer interfaces as it can provide similar spatial resolution to more invasive techniques, but reduces scar-tissue formation and hence enables longer-term recordings.
An integral part of every brain-machine interface system is an amplifier/digitizer system that converts the brain activity picked up by the electrodes to digital signals for further processing and/or transmission. The main challenge in the design of such a subsystem is to provide low input-referred noise while avoiding loading excessively the high impedance electrodes and while preventing the large offset associated with the electrode-tissue interface from saturating the electronics. Current solutions design the amplifying and digitizing functions separately and use large passive components, leading to an un-economically large footprint for the electronics.
State-of-the-art ECoG and EEG amplifiers occupy a large portion of die area due not only to the input AC coupling capacitors employed but also to the feedback capacitors that are used to cancel the upmodulated offset at the summing node. While good power efficiencies have been achieved, the resulting die area per amplifier can make arrayed implementations beyond approximately eight amplifiers impractical. Accordingly, there is a need to be able to substantially shrink the die area of ECoG neural amplifiers and front-end circuits while maintaining or improving power efficiency.